Fix crash when clicking acknowledge button on fleet alert

- Stop countdown timer before closing form
- Add FormClosing event handler to ensure cleanup
- Bump tray version to 1.6.1

agent/ShopDbEndpointAgent.Tray/FleetAlertForm.cs

@@ -37,6 +37,12 @@ internal sealed class FleetAlertForm : Form
         ApplyRoundedCorners();
 
         Load += FleetAlertForm_Load;
+        FormClosing += FleetAlertForm_FormClosing;
+    }
+
+    private void FleetAlertForm_FormClosing(object? sender, FormClosingEventArgs e)
+    {
+        countdownTimer?.Stop();
     }
 
     private void FleetAlertForm_Load(object? sender, EventArgs e)
@@ -255,6 +261,7 @@ internal sealed class FleetAlertForm : Form
 
     private void AcknowledgeButton_Click(object? sender, EventArgs e)
     {
+        countdownTimer?.Stop();
         OnAcknowledgeClicked?.Invoke(this, EventArgs.Empty);
         DialogResult = DialogResult.OK;
         Close();
@@ -262,6 +269,7 @@ internal sealed class FleetAlertForm : Form
 
     private void CloseButton_Click(object? sender, EventArgs e)
     {
+        countdownTimer?.Stop();
         OnAcknowledgeClicked?.Invoke(this, EventArgs.Empty);
         DialogResult = DialogResult.OK;
         Close();

agent/ShopDbEndpointAgent.Tray/ShopDbEndpointAgent.Tray.csproj

@@ -71,7 +71,9 @@
 			  copies of the exit-code handling. A tray that cannot open the channel
 			  logs and keeps its timer, so the failure mode is "refresh is not
 			  immediate", not "session data stops working". Requires agent 1.11.0. -->
-		 <Version>1.6.0</Version>
+		 <!-- 1.6.1: fix crash when clicking acknowledge button. The countdown timer
+	     is now properly stopped before the form closes to prevent disposal issues. -->
+	<Version>1.6.1</Version>
 	<InvariantGlobalization>true</InvariantGlobalization>
 	<RuntimeIdentifier>win-x64</RuntimeIdentifier>
 	<SelfContained>true</SelfContained>